This has already been explained. Only x amount of tickets are sold per x square feet. As you can see, all of the people are pushed forward. If they were to spread out and stand the way they are supposed to, it would look full. Furthermore, the sound and lighting engineer booth is in the crowd right behind the GA. As you can see, every seat is filled, so it's not because they couldn't fill the GA. In other crowd pictures from the tour, you see the same exact thing for the sold out shows.
Here's the crowd at a sold out show during The Monster Ball.
